"If you can keep going and playing the way that you are and your opponent's not feeling so great, it's even easier to keep going.

"Whereas if you give them that little bit of a sniff, things can start going better, it can become a tight one."

Pironkova had been on a nine-match winning streak but was no match for Stosur after taking a medical time-out for her leg injury after the opening set.

Even after having her left thigh strapped, the newly-crowned Sydney International champion was unable to move freely and barely challenged Stosur.

Stosur's comfortable win thrust her into the third round at Melbourne Park for the first time since winning the 2011 US Open.

Pironkova was expected to trouble Stosur after entering their second-round contest in the form of her life.

The 25-year-old knocked over three top 10 stars in marching to the Sydney title from qualifying last week.

But the heavy workload of eight matches in nine days - plus a first-round victory in Melbourne - ultimately took its toll on the one-time Wimbledon semi-finalist.

Stosur broke her twice to take the first set in 39 minutes and then won 13 successive points at the start of the second.

Pironkova, the world number 57, must have known defeat was inevitable but gallantly played on, perhaps mindful that the Rod Laver Arena crowd were short-changed the previous night when Bernard Tomic retired after just one set with a groin tear.

The Bulgarian won just eight points in total in the second set before Stosur put her out of her misery after 64 uncomfortable minutes on court.

Aussie Ebden bows out of men's draw

Stosur's compatriot Matt Ebden exited the men's draw in the second round, losing in four sets to Canadian 28th seed Vasek Pospisil.

Pospisil appeared to struggle in the first two sets with a back injury and twice took a medical timeout for treatment.

The 28th seed said post-match he considered withdrawing until pain killers kicked in to get him over the line 3-6, 7-6 (8/6), 7-6 (11/9), 6-1.

But Ebden, who was clearly unsettled by his opponent's up-and-down form, sounded sceptical about the injury.

"I guess I got a bit tricked," the Western Australian said.

"I'm puzzled. I felt he was struggling a bit but then he was serving amazing, over 200km, and moving side to side so I guess that's on me.

"I tried to do everything I could but it just didn't fall my way.

"I'm obviously pretty unhappy about it."

He set up a third-round date with Swiss eighth seed Stanislas Wawrinka who fought past Alejandro Falla of Colombia in four sets, winning 6-3, 6-3, 6-7 (4-7), 6-4.

Earlier in the evening Wawrinka's fellow seeds Fabio Fognini (15) and Kevin Anderson (19) also moved through to the third round.